ci: Remove `migration_checks` as a required check (#26833)
Marshall Bowers
created
This PR removes the `migration_checks` job as a required check.
This was not required before, and we shouldn't make it required, as
there are cases where we need to bypass it, as is the case in
https://github.com/zed-industries/zed/pull/26832.
Release Notes:
- N/A